JP2020173946A - Lithium-sulfur solid-state battery - Google Patents

Abstract

To provide a lithium-sulfur solid-state battery that suppresses the solid electrolyte from being reduced by contacting a lithium negative electrode and metal ions reduced by sulfur such as titanium and germanium contained in a solid electrolyte, and suppresses the battery performance from deteriorating.SOLUTION: A lithium-sulfur solid-state battery 1 includes a sulfur positive electrode 11, a lithium negative electrode 12, and a solid electrolyte 13 including metal ions reduced by sulfur, and a lithium ion conductive layer, and the solid electrolyte 13 is arranged between the sulfur positive electrode 11 and the lithium negative electrode 12, and the lithium ion conductive layer includes a first lithium ion conductive layer 14 between the solid electrolyte 13 and the sulfur positive electrode 11, and a second lithium ion conductive layer 15 between the solid electrolyte 13 and the lithium negative electrode 12, and the first lithium ion conductive layer 14 includes an ionic liquid and conducts lithium ions between the solid electrolyte 13 and the sulfur positive electrode 11, and the second lithium ion conductive layer 15 includes an ionic liquid and conducts lithium ions between the solid electrolyte 13 and the lithium negative electrode 12.SELECTED DRAWING: Figure 1

Description

The present invention relates to a lithium-sulfur solid-state battery.

In recent years, portable and cordless electronic devices and communication devices have been rapidly progressing. As a power source for these electronic devices and communication devices, secondary batteries with high energy density and excellent load characteristics are required, and lithium ion secondary batteries with high voltage, high energy density, and excellent cycle characteristics are used. It is expanding.
On the other hand, batteries with even higher energy densities are required for the spread of electric vehicles and the promotion of the use of natural energy. Therefore, it is desired to develop a new lithium ion secondary battery that replaces the lithium ion secondary battery in which a lithium composite oxide such as LiCoO _{2 is} used as a constituent material of the positive electrode.

Sulfur has an extremely high theoretical capacity density of 1672 mAh / g, and a lithium-sulfur battery using sulfur as a constituent material of the positive electrode has the potential to achieve the theoretically highest energy density among batteries. ing. Therefore, research and development of lithium-sulfur batteries have been actively carried out.

As an electrolyte for a lithium-sulfur battery, it has been studied to use a solid electrolyte containing titanium, germanium, aluminum, etc., which has high ionic conductivity and is easy to handle in the atmosphere (see, for example, Non-Patent Documents 1 and 2).

Lina Wang, Yonggang Wang and Yongyao Xia, "Towards high performance lithium-ion sulfur battery battery base on Li2S cathode chemistry chemistry Name. , 2015,00, 1-3. Kota Suzuki, Dai Kato, Kusuke Hara, Taka-aki Yano, Masaaki Hirayama, Masahiko Hara and Royji Kanno, "Composite Sulfur Electrode for All-solid-state Lithium-sulfur Battery with Li2S-GeS2-P2S5-based Thio-LISICON Solid Electrolyte , The Electrochemical Society of Japan 2017.

However, when the positive electrode containing sulfur (sulfur positive electrode) comes into contact with metal ions reduced by sulfur such as titanium and germanium contained in the solid electrolyte, the solid electrolyte is reduced and the battery performance is deteriorated. Therefore, the solid electrolyte is described above. There is a problem that it is difficult to construct a battery equipped with a sulfur positive electrode.

The present invention has been made in view of the above circumstances, and the solid electrolyte is reduced by contacting the sulfur positive electrode with metal ions reduced by sulfur such as titanium and germanium contained in the solid electrolyte. An object of the present invention is to provide a lithium-sulfur solid-state battery in which deterioration of battery performance is suppressed.

In order to solve the above problems, the present invention adopts the following configuration.
[1]. A sulfur positive electrode, a lithium negative electrode, a solid electrolyte containing metal ions reduced by sulfur, and a lithium ion conductive layer are provided, and the solid electrolyte is arranged between the sulfur positive electrode and the lithium negative electrode. The lithium ion conductive layer includes a first lithium ion conductive layer arranged between the solid electrolyte and the sulfur positive electrode, and a second lithium ion conductive layer arranged between the solid electrolyte and the lithium negative electrode. The first lithium ion conductive layer contains an ionic liquid and conducts lithium ions between the solid electrolyte and the sulfur positive electrode, and the second lithium ion conductive layer contains an ionic liquid. A lithium sulfur solid battery that conducts lithium ions between the solid electrolyte and the lithium negative electrode.

[2]. The lithium-sulfur solid-state battery according to [1], wherein the first lithium ion conductive layer contains polyimide or glass as a constituent material thereof.
[3]. The lithium-sulfur solid-state battery according to [1] or [2], wherein the ionic liquid is a solvated ionic liquid composed of a glyme-lithium salt complex.
[4]. The lithium-sulfur solid-state battery according to any one of [1] to [3], wherein the constituent material of the solid electrolyte is an oxide-based material.

According to the present invention, the contact between the sulfur positive electrode and the metal ions reduced by sulfur such as titanium and germanium contained in the solid electrolyte reduces the solid electrolyte and suppresses the deterioration of the battery performance. A sulfur solid state battery can be provided.

It is sectional drawing which shows typically an example of the main part of the lithium-sulfur solid-state battery which concerns on one Embodiment of this invention. It is a figure which shows the constant current discharge test of the battery cell obtained in an Example. It is a figure which shows the constant current discharge test of the battery cell obtained in the comparative example. It is a photograph which shows the solid electrolyte before the constant current charge / discharge test. It is a photograph which shows the solid electrolyte after a constant current charge / discharge test.

<< Lithium-sulfur solid-state battery >>
The lithium sulfur solid battery according to the embodiment of the present invention includes a sulfur positive electrode, a lithium negative electrode, a solid electrolyte containing metal ions reduced by sulfur, and a lithium ion conductive layer, and the solid electrolyte is the above-mentioned solid electrolyte. The lithium ion conductive layer is arranged between the sulfur positive electrode and the lithium negative electrode, and the lithium ion conductive layer is a first lithium ion conductive layer arranged between the solid electrolyte and the sulfur positive electrode, and the solid electrolyte and the lithium negative electrode. The first lithium ion conductive layer contains an ionic liquid and conducts lithium ions between the solid electrolyte and the sulfur positive electrode, including a second lithium ion conductive layer arranged between the two. The second lithium ion conductive layer contains an ionic liquid and conducts lithium ions between the solid electrolyte and the lithium negative electrode.
The lithium-sulfur solid battery of the present embodiment includes the first lithium ion conductive layer between the solid electrolyte containing metal ions reduced by contact with sulfur such as titanium and germanium and the sulfur positive electrode. As a result, the sulfur positive electrode and the solid electrolyte do not come into direct contact with each other, and the electron conduction path is blocked. Therefore, it is possible to suppress the reduction of the solid electrolyte, specifically, metal ions such as titanium and germanium. As a result, deterioration of battery performance can be suppressed.

Hereinafter, first, the structure of the lithium-sulfur solid-state battery of the present embodiment will be described in detail with reference to the drawings.
In addition, in the figure used in the following description, in order to make it easy to understand the features of the present invention, the main part may be enlarged for convenience, and the dimensional ratio of each component is the same as the actual one. Is not always the case.

FIG. 1 is a cross-sectional view schematically showing an example of a main part of the lithium-sulfur solid-state battery of the present embodiment.
The lithium-sulfur solid-state battery 1 shown here is configured to include a sulfur positive electrode 11, a lithium negative electrode 12, a solid electrolyte 13, a first lithium ion conductive layer 14, and a second lithium ion conductive layer 15. ..
In the lithium-sulfur solid-state battery 1, the solid electrolyte 13 is arranged between the sulfur positive electrode 11 and the lithium negative electrode 12, and the first lithium ion conductive layer 14 is arranged between the solid electrolyte 13 and the sulfur positive electrode 11. The 2 lithium ion conductive layer 15 is arranged between the solid electrolyte 13 and the lithium negative electrode 12. That is, in the lithium-sulfur solid-state battery 1, the sulfur positive electrode 11, the first lithium ion conductive layer 14, the solid electrolyte 13, the second lithium ion conductive layer 15, and the lithium negative electrode 12 are laminated in this order in the thickness direction. There is.

The first lithium ion conductive layer 14 is referred to from one surface (sometimes referred to as "first surface" in the present specification) 14a to the other surface (referred to as "second surface" in the present specification). It has a large number of voids (not shown) that reach up to 14b. Therefore, liquid substances and fine substances can be transferred between the sulfur positive electrode 11 and the solid electrolyte 13 via the first lithium ion conductive layer 14.
Further, the first lithium ion conductive layer 14 holds an ionic liquid (not shown) in the voids and the like. Lithium ions can be dissolved in this ionic liquid. Therefore, lithium ions can be easily conducted between the sulfur positive electrode 11 and the solid electrolyte 13 (in the direction of the thickness T14 in the first lithium ion conductive layer 14) via the first lithium ion conductive layer 14. It has become.

In the first lithium ion conductive layer 14, the portion having the void portion, holding the ionic liquid, and maintaining the shape of the lithium ion conductive layer is referred to as a “main body portion” in the present specification. .. That is, the first lithium ion conductive layer 14 includes the main body portion and the ionic liquid held by the main body portion.

The main body of the first lithium ion conductive layer 14 is, for example, a porous body or a fibrous material in which fibrous materials are aggregated to form a layer (in the present specification, "fiber aggregate". ”) Etc. can be mentioned.

The lithium-sulfur solid-state battery 1 is provided with the first lithium ion conductive layer 14 between the solid electrolyte 13 containing metal ions that are reduced by contact with sulfur such as titanium and germanium and the sulfur positive electrode 11. Since the sulfur positive electrode 11 and the solid electrolyte 13 do not come into direct contact with each other and the electron conduction path is blocked, it is possible to suppress the reduction of the solid electrolyte 13, specifically, metal ions such as titanium and germanium. As a result, deterioration of battery performance can be suppressed.

Further, in the lithium-sulfur solid-state battery 1, for example, the titanium ions contained in the solid electrolyte 13 are tetravalent to 3 due to the presence of the first lithium ion conducting layer 14 between the sulfur positive electrode 11 and the solid electrolyte 13. It is possible to suppress the reduction to the value. When the titanium ions contained in the solid electrolyte 13 are reduced from tetravalent to trivalent, the solid electrolyte 13 cannot be electrically neutralized, and lithium ions (Li ⁺ ) enter into the solid electrolyte 13. The solid electrolyte 13 changes to a compound having low ionic conductivity. As a result, battery performance deteriorates.

The second lithium ion conductive layer 15 is referred to from one surface (sometimes referred to as the "first surface" in the present specification) 15a to the other surface (in the present specification, the "second surface"). It has a large number of voids (not shown) that reach up to 15b. Therefore, liquid substances and fine substances can be transferred between the lithium negative electrode 12 and the solid electrolyte 13 via the second lithium ion conductive layer 15.
Further, the second lithium ion conductive layer 15 holds an ionic liquid (not shown) in the voids and the like. Lithium ions can be dissolved in this ionic liquid. Therefore, lithium ions can be easily conducted between the lithium negative electrode 12 and the solid electrolyte 13 (in the direction of the thickness T15 in the second lithium ion conductive layer 15) via the second lithium ion conductive layer 15. It has become.

The portion of the second lithium ion conductive layer 15 that has the void portion, holds the ionic liquid, and maintains the shape of the lithium ion conductive layer is referred to as a “main body portion” in the present specification. .. That is, the second lithium ion conductive layer 15 includes the main body portion and the ionic liquid held by the main body portion.

The main body of the second lithium ion conductive layer 15 is, for example, a porous body or a fibrous material in which fibrous materials are aggregated to form a layer (in the present specification, "fiber aggregate". ”) Etc. can be mentioned.

In the lithium sulfur solid battery 1, the presence of the second lithium ion conductive layer 15 between the solid electrolyte 13 and the lithium negative electrode 12 causes, for example, the solid electrolyte 13 containing metal ions containing titanium, germanium, and the like. Since the lithium metal 12 does not come into direct contact with each other and the electron conduction path is blocked, it is possible to suppress the reduction of the solid electrolyte 13, specifically, metal ions such as titanium and germanium. As a result, deterioration of battery performance can be suppressed.

In the lithium-sulfur solid-state battery 1, for example, the sulfur positive electrode 11 and the lithium negative electrode 12 are each provided with terminals for connection with an external circuit.
Further, in the lithium-sulfur solid-state battery 1, if necessary, the entire laminated structure of the above-mentioned sulfur positive electrode 11, the first lithium ion conductive layer 14, the solid electrolyte 13, the second lithium ion conductive layer 15 and the lithium negative electrode 12 is formed. , Stored in a container.
Further, the lithium-sulfur solid-state battery 1 further suppresses the leakage of the ionic liquids in the first lithium ion conductive layer 14 and the second lithium ion conductive layer 15 to the outside of the lithium sulfur solid-state battery 1, if necessary. A mechanism (leakage suppression mechanism) may be provided. For example, the container may also serve as such a leakage suppression mechanism.
Next, the configuration of each layer of the lithium-sulfur solid-state battery of the present embodiment will be described in detail.

<Sulfur positive electrode>
The sulfur positive electrode in the lithium-sulfur solid-state battery of the present embodiment is not particularly limited as long as it contains sulfur and functions as a positive electrode.
Examples of the sulfur positive electrode include known ones in which a positive electrode active material layer is provided on a current collector (positive electrode current collector).

However, as a preferable sulfur positive electrode, for example, a conductive sheet having a large number of voids is provided, the voids are open to the outside of the conductive sheet, and the conductive sheet is formed in the voids. , At least one containing sulfur, and it is preferable that the conductive sheet contains at least sulfur and an ionic liquid in the voids.
As such a sulfur positive electrode, for example, the conductive sheet contains sulfur, a conductive auxiliary agent, a binder and an ionic liquid in the void portion (in the present specification, "sulfur positive electrode (I)). The conductive sheet contains sulfur in the voids and does not contain a conductive auxiliary agent and a binder (in the present specification, "sulfur positive electrode (II)". (Sometimes referred to as). The sulfur positive electrode (II) preferably further contains an ionic liquid in the voids.
Hereinafter, these constituent materials of the sulfur positive electrode will be described in detail for each sulfur positive electrode.

○ Sulfur positive electrode (I)
[Conductive sheet]
In the sulfur positive electrode (I), the conductive sheet can function as a positive electrode current collector.
The voids in the conductive sheet hold components other than the conductive sheet of the sulfur positive electrode (I), that is, sulfur, a conductive auxiliary agent, a binder, and an ionic liquid. Then, the conductive sheet can function as a positive electrode current collector.
Further, the gap portion is open to the outside of the conductive sheet, and it is possible to retain these components by adding various components such as sulfur to the conductive sheet later. There is.

The shape of the void portion in the conductive sheet is not particularly limited as long as the above conditions are satisfied.
For example, the voids may be connected to one or more other voids, or may be independent without being connected to the other voids.
Further, both the connected voids and the non-connected voids may or may not penetrate from one surface of the conductive sheet to the other surface on the opposite side, and are conductive without penetrating. There may be a dead end inside the sex sheet.
Further, both the connected voids and the non-connected voids may reach the same surface again from one surface of the conductive sheet via the inside of the conductive sheet.

The form of the conductive sheet is, for example, a porous body or a fiber aggregate (a fibrous material in which fibrous materials are aggregated to form a layer) similar to the main body of the lithium ion conductive layer described above. And so on. The fiber aggregate constituting the conductive sheet may be, for example, one in which fibrous materials are entwined with each other, or one in which fibrous materials are regularly or irregularly stacked. You may.

The constituent material of the conductive sheet may have conductivity, but is preferably one that does not have reactivity with sulfur.
More specific examples of the constituent material of the conductive sheet include carbon, metal (elemental metal, alloy) and the like.
Among them, preferable constituent materials of the conductive sheet include constituent materials of the positive electrode current collector, and more specifically, for example, carbon, copper, aluminum, titanium, nickel, stainless steel and the like.

The constituent materials of the conductive sheet may be only one kind, two or more kinds, and when there are two or more kinds, the combination and the ratio thereof can be arbitrarily selected according to the purpose.

Preferred conductive sheets include, for example, carbon felt, carbon cloth and the like.

The thickness of the conductive sheet is not particularly limited, and may be appropriately set according to the purpose of the battery to be applied. Usually, the thickness of the conductive sheet is preferably 50 μm to 30,000 μm, more preferably 100 μm to 3000 μm.

When the thickness of the conductive sheet clearly varies depending on the part of the conductive sheet, such as when the surface of the conductive sheet has a high degree of unevenness, the maximum thickness is defined as the thickness of the conductive sheet. (The thickness of the thickest part of the conductive sheet is defined as the thickness of the conductive sheet). This is the same not only for the conductive sheet but also for the thickness of all the layers (sulfur positive electrode, lithium negative electrode, solid electrolyte and lithium ion conductive layer described later).

[Conductive aid]
The conductive auxiliary agent may be a known one, and specific examples thereof include graphite (graphite); carbon black such as Ketjen black and acetylene black; carbon nanotube; graphene; fullerene and the like.
The conductive auxiliary agent contained in the sulfur positive electrode (I) may be only one type, two or more types, and when two or more types, the combination and ratio thereof can be arbitrarily selected according to the purpose.

The ratio of the total content of sulfur and conductive auxiliary agent to the total content of sulfur, conductive auxiliary agent, binder and ionic liquid in the sulfur positive electrode (I) ([total content of sulfur and conductive auxiliary agent in sulfur positive electrode (I)). Amount (parts by mass)] / [total content of sulfur, conductive additive, binder and ionic liquid in the sulfur positive electrode (I) (parts by mass)] × 100) is not particularly limited, but is 60% by mass to 95% by mass. It is preferably 70% by mass to 85% by mass, and more preferably 70% by mass to 85% by mass. When the ratio of the total content is at least the lower limit value, the charge / discharge characteristics of the battery are further improved. When the ratio of the total content is not more than the upper limit value, the effect of using the components other than sulfur and the conductive auxiliary agent can be obtained more remarkably.

In the sulfur positive electrode (I), the mass ratio of [sulfur content (parts by mass)]: [content of conductive aid (parts by mass)] is not particularly limited, but is 30:70 to 70:30. Is preferable, and 45:55 to 65:35 is more preferable. The higher the ratio of the sulfur content, the better the charge / discharge characteristics of the battery, and the higher the ratio of the content of the conductive auxiliary agent, the more the conductivity of the sulfur positive electrode (I) is improved.

In the sulfur positive electrode (I), the sulfur and the conductive auxiliary agent may form a complex.
For example, a sulfur-carbon composite can be obtained by mixing sulfur and a carbon-containing material (for example, Ketjen black, etc.) and firing. Such a composite is also suitable as a component contained in the sulfur positive electrode (I).

[binder]
The binder may be a known one, and specific examples thereof include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-propylene hexafluoride copolymer (PVDF-HFP), and polyacrylic acid (PAA). Lithium polyacrylate (PAALI), styrene butadiene rubber (SBR), polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyethylene glycol (PEG), carboxymethyl cellulose (CMC), polyvinylidene nitrile (PAN), polyimide (PI) And so on.
The binder contained in the sulfur positive electrode (I) may be only one type, may be two or more types, and when there are two or more types, the combination and ratio thereof can be arbitrarily selected according to the purpose.

In the sulfur positive electrode (I), the ratio of the content of the binder to the total content of sulfur, the conductive auxiliary agent, the binder and the ionic liquid ([content of the binder of the sulfur positive electrode (I) (parts by mass)] / [sulfur positive electrode). The total content (parts by mass) of the sulfur, the conductive auxiliary agent, the binder and the ionic liquid of (I) is not particularly limited, but is preferably 3% by mass to 15% by mass, and 5% by mass to 5% by mass. It is more preferably 9% by mass. When the content ratio is at least the lower limit value, the structure of the sulfur positive electrode (I) can be maintained more stably. When the content ratio is not more than the upper limit value, the charge / discharge characteristics of the battery are further improved.

[Ionic liquid]
The ionic liquid contained in the sulfur positive electrode (I) is a component for easily moving lithium ions, and is excellent in high temperature stability. Since the sulfur positive electrode (I) contains an ionic liquid, the contact area between the sulfur positive electrode (I) and the solid electrolyte is small, but the ionic liquid produces lithium ions between the sulfur positive electrode (I) and the solid electrolyte. Move. Therefore, the solid-state battery using the sulfur positive electrode (I) has a small interface resistance value at the sulfur positive electrode interface and has excellent battery characteristics even though the solid electrolyte is used.

The ionic liquid can be appropriately selected from, for example, known ones.
However, as the ionic liquid, for example, a liquid having a low sulfur solubility in a temperature range of less than 170 ° C. is preferable, and a liquid that does not dissolve sulfur is particularly preferable.

Examples of the ionic liquid include an ionic compound that is liquid at a temperature of less than 170 ° C., a solvated ionic liquid, and the like.

(Ionic compounds that are liquid at temperatures below 170 ° C)
The cation portion constituting the ionic compound may be either an organic cation or an inorganic cation, but is preferably an organic cation.
The anion portion constituting the ionic compound may be either an organic anion or an inorganic anion.

Among the cation portions, examples of the organic cation include an imidazolium cation, a pyridinium cation, a pyrrolidinium cation, a sulfonium cation, and an ammonium cation. , Sulfonium cation, and the like.
However, the organic cation is not limited to these.

Wherein among the anion portion, the organic anion, e.g., methylsulfate anion _(CH 3 SO ₄ ^-), ethylsulfate anion ^{_{(C 2 H 5 SO 4 -}} ) alkyl sulfate anion (alkylsulfate anion) such as; tosylate anion ( CH ₃ C ₆ H ₄ SO ₃ ⁻ ); Alcans such as methanesulfonate anion (CH ₃ SO ₃ ⁻ ), ethane sulfonate anion (C ₂ H ₅ SO ₃ ⁻ ), butane sulfonate anion (C ₄ H ₉ SO ₃ ⁻ ) Alkanesulfonate anion; trifluoromethanesulfonate anion (CF ₃ SO ₃ ⁻ ), pentafluoroethane sulfonate anion (C ₂ F ₅ SO ₃ ⁻ ), heptafluoropropane sulfonate anion (C ₃ H ₇ SO ₃ ⁻ ), nona Perfluoroalkanesulfonate anions such as fluorobutane sulfonate anion (C ₄ H ₉ SO ₃ ⁻ ); bis (trifluoromethanesulfonyl) imide anion ((CF ₃ SO ₂ ) N ⁻ ), bis (nonafluorobutane sulfonyl). ) imide anion _{((C 4 F 9 SO 2} ) N -), nonafluoro -N - [(trifluoromethane) sulfonyl] butane sulfonyl imide anion _{((CF 3 SO 2) (} C 4 F 9 SO 2) N -), N, N-hexafluoro-1,3-imide anion _{(SO 2 CF 2 CF 2 CF} 2 SO 2 N -) perfluoroalkanesulfonyl anion (perfluoroalkanesulfonylimide anion) such as; acetate anion _(CH 3 COO ^-) ; hydrogen sulfate anion (HSO ₄ ^-); and the like.
However, the organic anion is not limited to these.

Among the anion portion, the inorganic anions include bis (fluorosulfonyl) imide anion _{(N (SO 2 F) 2} -); hexafluorophosphate anion (PF ₆ ^-); tetrafluoroborate anion (BF ₄ ^-) ; chloride ion (Cl ^-), bromide ion (Br ^-), iodide ion (I ^-) halide anions such (halide anion); tetrachloroaluminate anion (AlCl ₄ ^-), thiocyanate anion (SCN ^-) and the like Can be mentioned.
However, the inorganic anion is not limited to these.

Examples of the ionic compound include those composed of a combination of any of the above-mentioned cation portions and any of the above-mentioned anion portions.

Examples of the ionic liquid in which the cation part is an imidazolium cation include 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide, 1-butyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide, and 1 -Methyl-3-propylimidazolium bis (trifluoromethanesulfonyl) imide, 1-hexyl-3-methylimidazoliumbis (trifluoromethanesulfonyl) imide, 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-3 Methyl imidazolium chloride, 1-ethyl-3-methyl imidazolium methanesulfonate, 1-butyl-3-methyl imidazolium methane sulfonate, 1,2,3-trimethyl imidazolium methyl sulfate, methyl imidazolium chloride, methyl imidazolium hydro Gensulfate, 1-ethyl-3-methylimidazolium hydrogensulfate, 1-butyl-3-methylimidazolium hydrogensulfate, 1-butyl-3-methylimidazolium hydrogensulfate, 1-ethyl-3-methylimidazole Rium tetrachloroaluminate, 1-butyl-3-methylimidazolium tetrachloroaluminate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazole Rium ethyl sulfate, 1-butyl-3-methylimidazolium methyl sulfate, 1-ethyl-3-methylimidazolium thiocyanate, 1-butyl-3-methylimidazolium thiocyanate, 1-ethyl-2,3-dimethylimidazolium ethyl Sulfate and the like can be mentioned.

Examples of the ionic liquid in which the cation portion is a pyridinium cation include 1-butylpyridinium bis (trifluoromethanesulfonyl) imide and 1-butyl-3-methylpyridinium bis (trifluoromethanesulfonyl) imide.

Examples of the ionic liquid in which the cation portion is a pyrrolidinium cation include 1-methyl-1-propylpyrrolidinium bis (trifluoromethanesulfonyl) imide and 1-butyl-1-methylpyrrolidinium bis (trifluoromethanesulfonyl). Examples include imide and the like.

Examples of the ionic liquid in which the cation portion is a phosphonium cation include tetrabutylphosphonium bis (trifluoromethanesulfonyl) imide and tributyldodecylphosphonium bis (trifluoromethanesulfonyl) imide.

Examples of the ionic liquid in which the cation portion is an ammonium cation include methyltributylammoniummethylsulfate, butyltrimethylammonium bis (trifluoromethanesulfonyl) imide, and trimethylhexyl ammonium bis (trifluoromethanesulfonyl) imide.

(Solvation ionic liquid)
Preferred solvated ionic liquids include, for example, those composed of a grime-lithium salt complex.

Examples of the lithium salt in the glyme-lithium salt complex include lithium bis (fluorosulfonyl) imide (LiN (SO ₂ F) ₂ , which may be abbreviated as "LiFSI" in the present specification) and lithium bis (. Examples thereof include trifluoromethanesulfonyl) imide (LiN (SO ₂ CF ₃ ) ₂ , which may be abbreviated as “LiTFSI” in this specification).

Examples of the grime in the grime-lithium salt complex include triethylene glycol dimethyl ether (CH ₃ (OCH ₂ CH ₂ ) ₃ OCH ₃ , triglime), tetraethylene glycol dimethyl ether (CH ₃ (OCH ₂ CH ₂ ) ₄ OCH ₃ , and so on. Tetraglyclime) and the like.

Examples of the grime-lithium salt complex include, but are not limited to, a complex composed of one molecule of grime and one molecule of lithium salt.

The grime-lithium salt complex is prepared by mixing, for example, a lithium salt and a grime so that the molar ratio of lithium salt (mol): grime (mol) is preferably 10:90 to 90:10. Can be made.

Preferred grime-lithium salt complexes include, for example, triglyme-LiFSI complex, tetraglyme-LiFSI complex, triglyme-LiTFSI complex, tetraglyme-LiTFSI complex and the like.

The ionic liquid contained in the sulfur positive electrode (I) may be only one type, may be two or more types, and when there are two or more types, the combination and ratio thereof can be arbitrarily selected according to the purpose.

Among the above, the ionic liquid contained in the sulfur positive electrode (I) is preferably a solvated ionic liquid composed of a glyme-lithium salt complex.

The ratio of the content of the ionic liquid to the total content of sulfur, the conductive additive, the binder and the ionic liquid in the sulfur positive electrode (I) ([Content of the ionic liquid in the sulfur positive electrode (I) (parts by mass)] / [ The total content (parts by mass) of sulfur, conductive additive, binder and ionic liquid of the sulfur positive electrode (I) is not particularly limited, but is preferably 5% by mass to 20% by mass, preferably 9% by mass. More preferably, it is% to 15% by mass. When the content ratio is at least the lower limit value, the conductivity of the sulfur positive electrode (I) is further improved. When the content ratio is not more than the upper limit value, the charge / discharge characteristics of the battery are further improved.

[Other ingredients]
As long as the effect of the present invention is not impaired, the sulfur positive electrode (I) contains other components (however, a solvent described later) in addition to sulfur, a conductive auxiliary agent, a binder and an ionic liquid as constituent components other than the conductive sheet. (Excluding) may be contained.
The other components are not particularly limited and can be arbitrarily selected depending on the intended purpose.
The other components contained in the sulfur positive electrode (I) may be only one kind, two or more kinds, and when two or more kinds, the combination and ratio thereof can be arbitrarily selected according to the purpose.

In the sulfur positive electrode (I), the ratio of the content of the other components to the total content of sulfur, the conductive auxiliary agent, the binder and the ionic liquid ([content of other components of the sulfur positive electrode (I) (parts by mass)). ] / [Total content of sulfur, conductive auxiliary agent, binder and ionic liquid of the sulfur positive electrode (I) (parts by mass)] × 100) is not particularly limited, but is preferably 10% by mass or less, and 5% by mass. % Or less, more preferably 3% by mass or less, particularly preferably 1% by mass or less, and may be 0% by mass.

In the sulfur positive electrode (I), the ratio of the total mass of sulfur, conductive auxiliary agent, binder and ionic liquid to the mass of the conductive sheet ([total mass of sulfur, conductive auxiliary agent, binder and ionic liquid] / [conductive sheet [Mass] × 100) is preferably 15% by mass to 45% by mass, and more preferably 25% by mass to 40% by mass.

-Method of manufacturing the sulfur positive electrode (I) The sulfur positive electrode (I) is manufactured by a manufacturing method including a step of impregnating the conductive sheet with a positive electrode material containing, for example, sulfur, a conductive auxiliary agent, a binder and an ionic liquid. it can. The manufacturing method may further include other steps such as a step of drying the impregnated positive electrode material. Hereinafter, a method for producing such a sulfur positive electrode will be described.

[Positive material]
Preferred positive electrode materials include, for example, those containing sulfur, a conductive additive, a binder, an ionic liquid, a solvent, and, if necessary, the other components.

The solvent is a component for dissolving or dispersing each component such as the above-mentioned sulfur and imparting appropriate fluidity to the positive electrode material.
In the present specification, unless otherwise specified, no ionic liquid is included in the solvent (all ionic liquids are not treated as a solvent).

The solvent can be arbitrarily selected according to the type of each component such as sulfur described above, and an organic solvent is preferable.
Examples of the organic solvent include alcohols such as methanol, ethanol, 1-propanol and 2-propanol; amides such as N-methylpyrrolidone (NMP) and N, N-dimethylformamide (DMF); and ketones such as acetone. Can be mentioned.
The solvent contained in the positive electrode material may be only one type, may be two or more types, and when there are two or more types, the combination and ratio thereof can be arbitrarily selected according to the purpose.
The content of the solvent of the positive electrode material is not particularly limited, and can be appropriately adjusted according to the type of the component other than the solvent.

Ratio of sulfur content to total content of non-solvent components in the positive electrode material ([Sulfur content (mass) of positive electrode material] / [Total content of non-solvent components in positive electrode material (parts by mass) )] × 100) is the ratio of the sulfur content to the total content of sulfur, conductive aid, binder, ionic liquid and other components in the sulfur positive electrode ([Sulfur content (mass part) of the sulfur positive electrode). )] / [Total content of sulfur, conductive auxiliary agent, binder, ionic liquid and other components of the sulfur positive electrode (parts by mass)] × 100). This also applies to conductive auxiliaries, binders, ionic liquids and other components other than sulfur.

The positive electrode material can be obtained by blending each component such as sulfur described above.
The order of addition of each component at the time of blending is not particularly limited, and two or more kinds of components may be added at the same time.
When a solvent is used, the solvent is mixed with any component other than the solvent (ie, any component of the sulfur, conductive aid, binder, ionic liquid and other components described above) to mix this component. It may be used by diluting it in advance, or it may be used by mixing a solvent with these components without diluting any component other than the above-mentioned solvent in advance.

The method of mixing each component at the time of blending is not particularly limited, and known methods such as a method of rotating a stirring rod, a stirrer, a stirring blade, etc.; a method of mixing using a mixer; a method of adding ultrasonic waves to mix, etc. The method may be appropriately selected from the above methods.
The temperature and time at the time of adding and mixing each component are not particularly limited as long as each component does not deteriorate. Usually, the temperature at the time of mixing is preferably 15 ° C. to 30 ° C.

The composition obtained by adding and mixing each component may be used as it is as a positive electrode material, or some operation is performed on the obtained composition, for example, a part of the added solvent is removed by distillation or the like. The material obtained by adding the above may be used as the positive electrode material.

The impregnation of the positive electrode material into the conductive sheet can be performed by, for example, a method of applying a liquid positive electrode material to the conductive sheet, a method of immersing the conductive sheet in the liquid positive electrode material, or the like.
The positive electrode material can be applied to the conductive sheet by a known method.
The temperature of the positive electrode material impregnated into the conductive sheet is not particularly limited, but can be, for example, 15 ° C to 30 ° C. However, this is an example of the temperature.

The positive electrode material can be dried by a known method under normal pressure or reduced pressure. For example, it can be dried preferably under the conditions of 70 ° C. to 90 ° C. and 8 hours to 24 hours, but the drying conditions are not limited to this.

○ Sulfur positive electrode (II)
The sulfur positive electrode (II) contains sulfur in the void portion, and is obtained by impregnating a conductive sheet with molten sulfur or a sulfur solution.

[Conductive sheet]
The conductive sheet in the sulfur positive electrode (II) is the same as the conductive sheet in the sulfur positive electrode (I), and can be used in the same manner as in the case of the sulfur positive electrode (I).

[Sulfur, sulfur solution]
The sulfur solution is obtained by dissolving sulfur in a solvent.
The solvent of the sulfur solution is not particularly limited as long as it can dissolve sulfur and does not deteriorate the conductive sheet.
The solvent may be either an inorganic solvent or an organic solvent.
Examples of the inorganic solvent include carbon disulfide and the like.
Examples of the organic solvent include benzene, toluene, n-hexane and the like.

The solvent in the sulfur solution may be only one type, may be two or more types, and when there are two or more types, the combination and ratio thereof can be arbitrarily selected according to the purpose.

The concentration of sulfur in the sulfur solution is not particularly limited as long as the voids of the conductive sheet can be impregnated with the sulfur solution.
The concentration of sulfur in the sulfur solution can be appropriately adjusted depending on, for example, the type of solvent.
The sulfur concentration in the sulfur solution is preferably, for example, 0.1% by mass to 35% by mass. When the concentration is at least the lower limit value, a sulfur positive electrode (II) having a high sulfur content can be more easily obtained. When the concentration is not more than the upper limit value, the handleability of the sulfur solution at the time of impregnation of the conductive sheet becomes better.

At the time of producing the sulfur positive electrode (II), as a method of impregnating the conductive sheet with molten sulfur, for example, solid sulfur is placed on the surface of the conductive sheet and the sulfur in this state is heated. Method of melting (in this specification, it may be abbreviated as "impregnation method A"); method of supplying sulfur in a state of being melted by heating to the surface of a conductive sheet (in this specification, ". Impregnation method B ”may be abbreviated) and the like.
In the impregnation method A, for example, sulfur on the conductive sheet may be heated together with the conductive sheet.
In the impregnation method B, for example, the molten sulfur may be supplied to the surface of the conductive sheet while being heated. Further, sulfur may be supplied while heating the conductive sheet at a temperature equivalent to that of sulfur.

Among them, in the impregnation method A, the molten sulfur is naturally impregnated into the conductive sheet by gravity only by heating the sulfur on the conductive sheet, so that the impregnation can be performed extremely easily.
Therefore, the method of impregnating the conductive sheet with the molten sulfur is preferably the impregnation method A.

When the conductive sheet is impregnated with molten sulfur, the temperature of sulfur is preferably 120 ° C to 160 ° C, more preferably 135 ° C to 160 ° C, and preferably 150 ° C to 160 ° C. Especially preferable. When the temperature is in such a range, the melt viscosity of sulfur is sufficiently lowered, sulfur can be easily introduced into the voids of the conductive sheet, and the sulfur content in the voids becomes better. .. As a result, in the sulfur positive electrode (II), the conductive auxiliary agent and the binder usually used are not required, and the energy density of the lithium-sulfur solid-state battery becomes higher.

In the production of the sulfur positive electrode (II), as a method of impregnating the conductive sheet with the sulfur solution, for example, a method of supplying the sulfur solution to the surface of the conductive sheet; a method of immersing the conductive sheet in the sulfur solution, etc. Can be mentioned.

When the conductive sheet is impregnated with the sulfur solution, the temperature of the sulfur solution is preferably adjusted appropriately according to the type of the solvent in the sulfur solution. For example, the temperature of the sulfur solution is preferably equal to or lower than the boiling point of the solvent in the sulfur solution. When the temperature is not more than the upper limit value, the sulfur solution can be easily introduced into the voids of the conductive sheet, and the sulfur content in the voids becomes better. As a result, in the sulfur positive electrode (II), the conductive auxiliary agent and the binder usually used are not required, and the energy density of the lithium-sulfur solid-state battery becomes higher.

When the conductive sheet is impregnated with the sulfur solution, the lower limit of the temperature of the sulfur solution is not particularly limited as long as the sulfur solution does not solidify. For example, the temperature is preferably 15 ° C. or higher in terms of easy preparation of the sulfur solution and good handleability of the sulfur solution.

When the conductive sheet is impregnated with the sulfur solution, it is necessary to dry the sulfur solution (remove the solvent in the sulfur solution).
The sulfur solution may be dried by a known method, for example, under normal pressure, under reduced pressure, or under blowing conditions, or under any of the atmosphere and the atmosphere of an inert gas.
The drying temperature (solvent removal temperature) is preferably adjusted as appropriate according to the type of solvent in the sulfur solution. For example, the drying temperature of the sulfur solution is preferably equal to or higher than the boiling point of the solvent in the sulfur solution.

When the sulfur positive electrode (II) is obtained by impregnating a conductive sheet with molten sulfur or a sulfur solution, sulfur is contained in a unique state in the voids of the conductive sheet.
That is, sulfur is agglomerated in the voids of the conductive sheet, and is held in contact with the surface of the voids in a state where the generation of gaps is suppressed. In other words, in the voids of the conductive sheet, the massive sulfur has a large contact area with the surface of the voids. This is an effect that the molten sulfur or the sulfur solution is filled in the voids of the conductive sheet by impregnating the conductive sheet. For example, when the conductive sheet is impregnated with a sulfur dispersion containing undissolved sulfur, the undissolved sulfur is finally formed into particles or the like as it is in the voids of the conductive sheet. Be retained. In such a sulfur positive electrode (II), the contact area between the sulfur and the surface of the void portion becomes small.
In the lithium-sulfur solid-state battery of the present embodiment, in the sulfur positive electrode (II), the sulfur is contained in such a peculiar state, so that the conductive auxiliary agent and the binder usually used are not required, and the energy density is increased.

Further, in the sulfur positive electrode (II) of the present embodiment, the sulfur content can be increased more than in the case where the sulfur content is changed to a peculiar state. This is because the sulfur content in the voids of the conductive sheet increases. As described above, when the sulfur content is increased, the lithium-sulfur solid-state battery of the present embodiment uses a large amount of sulfur, and also has excellent battery characteristics in this respect.

As the sulfur positive electrode (II) in the present embodiment, for example, the sulfur content is preferably 6 mg / cm ² or more, more preferably 10 mg / cm ² or more, still more preferably 15 mg / cm ² or more, and particularly preferably 20 mg. / Cm ² or more can be mentioned. In the present specification, the "sulfur content (mg / cm ² ) of the sulfur positive electrode (II)" means that the sulfur positive electrode (II) is viewed in a plan view from directly above, unless otherwise specified. It means the sulfur content (mg) of the sulfur positive electrode (II) per 1 cm ² of the surface area of the sulfur positive electrode (II).

In the present embodiment, the upper limit of the sulfur content of the sulfur positive electrode (II) is not particularly limited. The sulfur content of the sulfur positive electrode (II) is preferably 300 mg / cm ² or less, for example, in that the sulfur positive electrode (II) can be more easily produced.

In the present embodiment, the sulfur content of the sulfur positive electrode (II) can be appropriately adjusted so as to be within a range set by arbitrarily combining the above-mentioned preferable lower limit value and upper limit value. For example, the content of sulfur of the sulfur cathode (II) ^is preferably ^{6mg / cm 2 ~300mg / cm 2} , more preferably from ^{10mg / cm 2 ~300mg / cm 2} , 15mg / cm 2 ~ still more preferably 300 mg / cm ^2, and particularly preferably ^{20mg / cm 2 ~300mg / cm 2} . However, these are examples of the sulfur content of the sulfur positive electrode (II).

As described above, due to the unique content of sulfur in the voids of the conductive sheet, the sulfur positive electrode (II) in the present embodiment is used as a normal positive electrode such as a conductive auxiliary agent and a binder. Ingredients are not required. As described above, it is possible to increase the sulfur content in the sulfur positive electrode (II) by not requiring (not containing) a component other than sulfur in the conductive sheet.

[Ionic liquid]
The sulfur positive electrode (II) preferably further contains an ionic liquid in the voids of the conductive sheet. The ionic liquid has excellent high-temperature stability and can easily move lithium ions. Therefore, since the sulfur positive electrode (II) contains an ionic liquid, the contact area between the sulfur positive electrode (II) and the solid electrolyte is small, but the ionic liquid is lithium between the sulfur positive electrode (II) and the solid electrolyte. Move the ions. Therefore, such a solid-state battery using the sulfur positive electrode (II) has a smaller interface resistance value at the sulfur positive electrode (II) interface and has better battery characteristics, even though the solid electrolyte is used. ..

The ionic liquid in the sulfur positive electrode (II) is the same as the ionic liquid in the sulfur positive electrode (I).

When an ionic liquid is used, the ratio of the content of the ionic liquid to the total content of sulfur and the ionic liquid in the sulfur positive electrode (II) ([content of the ionic liquid of the sulfur positive electrode (II) (parts by mass)] / [ The total content (parts by mass) of sulfur and ionic liquid of the sulfur positive electrode (II)] × 100) is not particularly limited, but is preferably 5% by mass to 95% by mass, and 10% by mass to 90% by mass. More preferably. When the ratio of the content is at least the lower limit value, the conductivity of the sulfur positive electrode (II) is further improved. When the content ratio is not more than the upper limit value, the charge / discharge characteristics of the battery are further improved.

In the sulfur positive electrode (II), an ionic liquid can be used as in the case of the sulfur positive electrode (I), except for the above points.

[Other ingredients]
The sulfur positive electrode (II) may contain other components that do not fall under any of the conductive sheet, sulfur, and ionic liquid, regardless of whether they are inside or outside the voids of the conductive sheet.
The other components are not particularly limited as long as they do not inhibit the function of the sulfur positive electrode (II).
The other components contained in the sulfur positive electrode (II) may be only one type, two or more types, and when two or more types, the combination and ratio thereof can be arbitrarily selected according to the purpose.
For example, the sulfur positive electrode (II) may contain a component used in a normal positive electrode, such as a conductive auxiliary agent and a binder. When the sulfur positive electrode (II) contains a conductive auxiliary agent, it may be contained as a composite of sulfur and the conductive auxiliary agent. The composite of sulfur and the conductive auxiliary agent is obtained by mixing, for example, sulfur and a carbon-containing material (for example, Ketjen black, etc.) and firing.

The conductive auxiliary agent in the sulfur positive electrode (II) is the same as the conductive auxiliary agent in the sulfur positive electrode (I).
The binder in the sulfur positive electrode (II) is the same as the binder in the sulfur positive electrode (I).

However, in the sulfur positive electrode (II), the higher the content of the other components, the lower the sulfur content.
From this point of view, in the sulfur positive electrode (II), the ratio of the content of the other components to the total content of the components other than the conductive sheet ([content (mass) of the other components in the sulfur positive electrode (II)). Part)] / [Total content of components other than the conductive sheet in the sulfur positive electrode (II) (parts by mass)] × 100) is preferably 10% by mass or less, and more preferably 5% by mass or less. It is preferably 3% by mass or less, more preferably 1% by mass or less, and most preferably 0% by mass, that is, the sulfur positive electrode (II) does not contain the other components. ..
In other words, in the sulfur positive electrode (II), the ratio of the total content of sulfur and ionic liquid to the total content of components other than the conductive sheet ([total content of sulfur and ionic liquid in the sulfur positive electrode (II) (mass)). Part)] / [Total content of components other than the conductive sheet in the sulfur positive electrode (II) (parts by mass)] × 100) is preferably 90% by mass or more, and more preferably 95% by mass or more. It is preferably 97% by mass or more, more preferably 99% by mass or more, and most preferably 100% by mass.
A lithium-sulfur solid-state battery satisfying such conditions has better battery characteristics.

Regardless of the type of the sulfur positive electrode, the thickness of the sulfur positive electrode is not particularly limited and may be appropriately set according to the purpose of the battery to be applied. Usually, the thickness of the sulfur positive electrode is preferably 100 μm to 30,000 μm, and more preferably 200 μm to 3000 μm.

<Lithium negative electrode>
The lithium negative electrode in the lithium-sulfur solid-state battery of the present embodiment may be a known one.

The thickness of the lithium negative electrode is not particularly limited, and may be appropriately set according to the purpose of the battery to be applied. Usually, the thickness of the lithium negative electrode is preferably 10 μm to 2000 μm, more preferably 100 μm to 1000 μm.

<Solid electrolyte>
The constituent material of the solid electrolyte in the lithium-sulfur solid-state battery of the present embodiment is not particularly limited as long as it contains metal ions reduced by sulfur such as titanium and germanium. Further, the constituent material of the solid electrolyte may be any of a crystalline material, an amorphous material and a glass material.

The constituent materials of the solid electrolyte may be only one kind, two or more kinds, and when there are two or more kinds, the combination and ratio thereof can be arbitrarily selected according to the purpose.

The constituent material of the solid electrolyte is preferably the oxide-based material from the viewpoint that a solid electrolyte having high stability in the atmosphere and high density can be produced.

The thickness of the solid electrolyte is not particularly limited, and may be appropriately set according to the purpose of the battery to be applied. Generally, the thickness of the solid electrolyte is preferably 10 μm to 1200 μm. When the thickness of the solid electrolyte is at least the above lower limit value, the manufacture and handleability thereof are improved. When the thickness of the solid electrolyte is not more than the upper limit value, the resistance value of the lithium-sulfur solid-state battery is further reduced.

The solid electrolyte can be produced, for example, by selecting a raw material such as a metal oxide, a metal hydroxide, or a metal sulfide according to the desired type, and firing or dusting the raw material. The amount of the raw material used may be appropriately set in consideration of the atomic number ratio of each metal in the solid electrolyte and the like.

<Lithium ion conductive layer>
As described above, the lithium ion conducting layer in the lithium-sulfur solid-state battery of the present embodiment contains an ionic liquid and lithium between the sulfur positive electrode and the solid electrolyte, and between the lithium negative electrode and the solid electrolyte. It is a layer that conducts ions.
As described above, the lithium ion conductive layer includes a main body portion and an ionic liquid.

[Main body]
Examples of the main body of the lithium ion conductive layer include a porous body and a fiber aggregate as described above.
The main body of the lithium ion conductive layer is preferably one that does not react with the lithium negative electrode, does not dissolve, and does not deteriorate under the temperature conditions during operation of the lithium sulfur solid-state battery. Here, "alteration of the main body" means that the composition of the components of the main body changes. The operating temperature of the lithium-sulfur solid-state battery can be appropriately set according to the type of the sulfur positive electrode. When a known sulfur positive electrode or sulfur positive electrode (I) is used, the operating temperature of the lithium-sulfur solid-state battery is, for example, preferably 110 ° C. or lower, more preferably 100 ° C. or lower. Therefore, the main body of the lithium ion conductive layer in this case is preferably stable under a temperature condition of, for example, about 120 ° C. On the other hand, when the sulfur positive electrode (II) is used, the operating temperature of the lithium-sulfur solid-state battery is preferably 110 ° C to 160 ° C. Therefore, the main body of the lithium ion conductive layer in this case is preferably one that is stable under such temperature conditions.

Among such main body portions, examples of the constituent material of the porous body or fiber aggregate include synthetic resin, glass, paper and the like, and synthetic resin or glass is preferable.
Among them, the constituent material of the main body is more preferably polyimide or glass. That is, it is more preferable that the lithium ion conductive layer contains polyimide or glass as its constituent material.

The constituent material of the main body of the lithium ion conductive layer may be only one type, may be two or more types, and when there are two or more types, the combination and ratio thereof can be arbitrarily selected according to the purpose.

[Ionic liquid]
Examples of the ionic liquid contained in the lithium ion conductive layer include those similar to the ionic liquid contained in the sulfur positive electrode described above (for example, an ionic compound liquid at a temperature of less than 170 ° C., a solvated ionic liquid, etc.).

The ionic liquid contained in the lithium ion conductive layer may be only one type, may be two or more types, and when there are two or more types, the combination and ratio thereof can be arbitrarily selected according to the purpose.

The ionic liquid contained in the lithium ion conductive layer may be the same as or different from the ionic liquid contained in the above-mentioned sulfur positive electrode.

The ionic liquid contained in the lithium ion conductive layer is preferably a solvated ionic liquid composed of a glyme-lithium salt complex.

The content of the ionic liquid in the lithium ion conductive layer is not particularly limited.
However, the ratio of the total volume of the ionic liquids held in the lithium ion conductive layer to the total volume of the voids in the main body of the lithium ion conductive layer ([total of the ionic liquids held in the lithium ion conductive layer]. Volume] / [total volume of voids in the main body of the lithium ion conductive layer] × 100) is preferably 80% by volume to 120% by volume at room temperature.
When the ratio is at least the lower limit value, the effect of suppressing the precipitation of metallic lithium in the solid electrolyte becomes higher. When the ratio is not more than the upper limit value, excessive use of the ionic liquid is suppressed.
The ratio can be larger than 100% by volume because the ionic liquid can be present in the lithium ion conductive layer in addition to the void portion of the main body portion.
In addition, in this specification, "normal temperature" means a temperature which is not particularly cooled or heated, that is, a normal temperature, and examples thereof include a temperature of 15 ° C. to 25 ° C.

The lithium ion conductive layer may be composed of one layer (single layer) or may be composed of two or more layers. When the lithium ion conductive layer is composed of a plurality of layers, the plurality of layers may be the same or different from each other, and the combination of the plurality of layers is not particularly limited.
In the present specification, not only in the case of the lithium ion conductive layer, "a plurality of layers may be the same or different from each other" means "all layers may be the same or all layers". May be different, or only some layers may be the same ", and" multiple layers are different from each other "means" at least one of the constituent materials and thicknesses of each layer is different from each other. It means "different".

The thickness of the lithium ion conductive layer (for example, in the case of the lithium sulfur solid-state battery 1 shown in FIG. 1, the thickness T14 of the first lithium ion conductive layer 14 and the thickness T15 of the second lithium ion conductive layer 15) is , Not particularly limited.
The thickness of the lithium ion conductive layer composed of a plurality of layers means the total thickness of all the layers constituting the lithium ion conductive layer.

However, the thickness of the lithium ion conductive layer is preferably 10 μm or more in that the suppression of Ti ion reduction in the solid electrolyte becomes higher. When the thickness of the lithium ion conductive layer is equal to or greater than the lower limit, metallic lithium does not precipitate in the lithium ion conductive layer, or even if a small amount of metallic lithium precipitates in the lithium ion conductive layer. Its effect does not extend to solid electrolytes. As a result, in the lithium-sulfur solid-state battery, the continuous precipitation of metallic lithium from the lithium ion conductive layer to the sulfur positive electrode via the solid electrolyte is suppressed.

On the other hand, the thickness of the lithium ion conductive layer is preferably 100 μm or less so that the thickness of the lithium ion conductive layer does not become excessive (more appropriate).
Generally, the thinner the lithium ion conductive layer, the lower the resistance value in the lithium ion conductive layer, and the higher the energy density of the lithium-sulfur solid-state battery.

For the lithium ion conductive layer, for example, a first raw material composition containing a constituent material of the main body, an ionic liquid, and a solvent if necessary is prepared, and the lithium ion conductive layer is formed on a surface to be formed. It can be formed by applying the first raw material composition and drying it if necessary. In this method, the main body and the lithium ion conductive layer are formed at the same time. When no solvent is used, it is not necessary to dry the coated first raw material composition.

At the time of preparing the first raw material composition, the temperature and time at the time of adding and mixing each raw material are not particularly limited as long as each raw material is not deteriorated. For example, the temperature at the time of mixing may be 15 ° C. to 50 ° C., which is an example. The method of mixing each raw material may be the same as the method of mixing each component at the time of producing the above-mentioned positive electrode material, for example.

The first raw material composition can be applied to the surface to be formed of the lithium ion conductive layer by a known method.
The temperature of the first raw material composition to be coated is not particularly limited as long as the surface to be formed of the lithium ion conductive layer, the constituent material of the main body, the ionic liquid, the solvent and the like are not deteriorated. For example, the temperature of the first raw material composition at this time may be 15 ° C. to 50 ° C., which is an example.

When the first raw material composition is dried, the drying can be carried out by a known method under normal pressure or reduced pressure. The drying temperature of the first raw material composition is not particularly limited and may be, for example, 20 ° C to 100 ° C, but this is an example.

When the surface to be formed of the lithium ion conductive layer is the arrangement surface of the lithium ion conductive layer in the lithium-sulfur solid-state battery (for example, the surface on the lithium negative electrode side of the solid electrolyte, the surface on the solid electrolyte side of the lithium negative electrode, etc.). The formed lithium ion conductive layer does not need to be moved to another place, and may be arranged as it is.
On the other hand, when the surface to be formed of the lithium ion conductive layer is not the surface on which the lithium ion conductive layer is arranged in the lithium sulfur solid state battery, the formed lithium ion conductive layer is peeled off from this surface to form the lithium sulfur solid state battery. It may be moved by sticking it to the target arrangement surface inside.

Further, for the lithium ion conductive layer, for example, an ionic liquid is impregnated in the main body, or a mixed solution containing the ionic liquid and a solvent is prepared, and the mixed solution is impregnated in the main body. It can also be formed by drying the main body after impregnation, if necessary. This method is a method using a pre-formed main body. When no solvent is used, it is not necessary to dry the main body after impregnation.
In this case, the main body is not arranged on the arrangement surface of the lithium ion conductive layer in the lithium-sulfur solid-state battery, but is handled independently to form the lithium ion conductive layer, and then the obtained lithium ions are obtained. It is preferable that the conductive layer is further attached to the target arrangement surface in the lithium-sulfur solid-state battery.

The main body can be produced by a known method, for example, by preparing a second raw material composition containing the constituent material of the main body and molding the second raw material composition.
Further, the main body may be a commercially available product.

Examples of the method of impregnating the main body with the ionic liquid or the mixed liquid include a method of applying the ionic liquid or the mixed liquid to the main body and immersing the main body in the ionic liquid or the mixed liquid. The method and the like can be mentioned.

The ionic liquid or mixed liquid can be applied to the main body by a known method.
The temperature of the ionic liquid or the mixed liquid impregnated in the main body is not particularly limited as long as the raw materials such as the main body, the ionic liquid and the solvent are not deteriorated. For example, the temperature of the ionic liquid or mixed liquid at the time of impregnation may be 15 ° C. to 50 ° C., which is an example.

The main body after impregnation with the mixed solution can be dried under normal pressure or reduced pressure by a known method. The drying temperature at this time is not particularly limited and may be, for example, 20 ° C to 100 ° C, but this is an example.

The lithium-sulfur solid-state battery of the present embodiment is not limited to the above, and has some configurations changed, deleted or added in the above-described ones without departing from the spirit of the present invention. It may be.

For example, the lithium-sulfur solid-state battery of the present embodiment has one type or two or more other layers, one layer for each type, which does not correspond to any of the sulfur positive electrode, the solid electrolyte, the lithium ion conductive layer, and the lithium negative electrode. Alternatively, two or more layers may be provided.
The other layer is not particularly limited as long as the effect of the present invention is not impaired, and can be arbitrarily selected depending on the intended purpose.

When a sulfur positive electrode composed of a component such as sulfur is used in the voids of the conductive sheet having a large number of voids, the lithium-sulfur solid-state battery of the present embodiment has a sulfur positive electrode and a solid electrolyte. , The lithium ion conductive layer and the lithium negative electrode are in direct contact with each other in this order (the other layers are not provided).

<< Manufacturing method of lithium-sulfur solid-state battery >>
In the lithium-sulfur solid cell of the present embodiment, the solid electrolyte is located between the sulfur positive electrode and the lithium negative electrode, and the lithium ion conductive layer is located between the solid electrolyte and the sulfur positive electrode, and the solid. It can be produced by a method having a step of arranging the sulfur positive electrode, the lithium negative electrode, the solid electrolyte and the lithium ion conductive layer so as to be located between the electrolyte and the lithium negative electrode.
In other words, in the lithium-sulfur solid-state battery of the present embodiment, the steps of laminating the sulfur positive electrode, the first lithium ion conductive layer, the solid electrolyte, the second lithium ion conductive layer and the lithium negative electrode in this order in the thickness direction thereof. It can be manufactured by the method of having.
For example, in the lithium-sulfur solid-state battery of the present embodiment, a lithium ion conductive layer is newly used, and the sulfur positive electrode, the first lithium ion conductive layer, the solid electrolyte, the second lithium ion conductive layer, and the lithium negative electrode are arranged as described above. It can be produced by the same method as in the case of a known lithium-sulfur solid-state battery, except that it is laminated on. When a sulfur positive electrode provided with the above-mentioned conductive sheet is used, a known lithium-sulfur solid-state battery is used except that such a sulfur positive electrode is additionally used instead of the conventional sulfur positive electrode. Can be manufactured in the same way as.

The handling temperature of the lithium-sulfur solid-state battery of the present embodiment is preferably 160 ° C. or lower. By doing so, the vaporization of the ionic liquid can be suppressed, and the lithium-sulfur solid-state battery exhibits more excellent battery characteristics.

The lithium-sulfur solid-state battery of the present embodiment has excellent battery characteristics as described above, and is highly safe. Taking advantage of these features, the lithium-sulfur solid-state battery is suitable for use as, for example, a household power source; an emergency power source; a power source for an airplane, an electric vehicle, or the like.

Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited to the following examples.

[Example]
(Manufacturing of solid electrolyte)
The LLT (Li _0.35 La _0.55 TiO ₃ ) powder, binder, auxiliary materials, and solvent were weighed, mixed to form a slurry, and pulverized with a ball mill.
The obtained slurry is defoamed and its viscosity is adjusted by a vacuum defoaming device, and the obtained slurry is thinly applied onto a PET film using a sheet molding machine, and then the contained solvent is volatilized to LLT. A resin sheet containing the powder of the above was obtained. Hereinafter, this is called a green sheet.
The blade height of the sheet molding machine was appropriately adjusted to prepare a green sheet having a thickness of 0.25 mm.
The produced green sheet was cut into an appropriate size in anticipation of firing shrinkage, and then fired in an atmospheric furnace to obtain an LLT thin plate (solid electrolyte) having a diameter of 17 mm and a thickness of 0.18 mm.

(Manufacturing of lithium ion conductive layer)
At room temperature, a porous polyimide sheet (diameter 18 mm, thickness 30 μm, porosity 74%) was immersed in a tetraglime-LiTFSI complex. The compounding ratio of tetraglime and LiTFSI in the tetraglime-LiTFSI complex was 1 mol: 1 mol.
Next, the glass fiber sheet was taken out from the tetraglime-LiTFSI complex to prepare a lithium ion conductive layer (thickness 30 μm).

(Manufacturing of battery cells)
The lithium ion conductive layer obtained above was attached to one surface of the LLT thin plate obtained above on the electrode side. Further, a sulfur positive electrode (diameter 8 mm, thickness 300 μm) was attached as a positive electrode to the surface of the LLT thin plate opposite to the surface on which the lithium ion conductive layer was attached. The sulfur positive electrode is obtained by melting sulfur at 130 ° C. and impregnating carbon cloth (diameter 8 mm, thickness 300 μm) with sulfur (21.8 mg / cm ² ).
Further, the lithium ion conductive layer obtained above was attached to the other surface of the LLT thin plate on the electrode side. Further, a lithium metal (diameter 15 mm, thickness 600 μm) was bonded to the surface of the lithium ion conductive layer on the side opposite to the LLT thin plate side as a negative electrode.
From the above, a laminate of a sulfur positive electrode, a lithium ion conductive layer, an LLT thin plate, a lithium ion conductive layer, and a lithium metal (negative electrode) was obtained.

Next, the laminate obtained above was placed in a commercially available stainless steel battery cell container, and finally the top lid was closed.
From the above, a battery cell for evaluation was obtained.

[Comparison example]
(Manufacturing of battery cells)
A laminate of a sulfur positive electrode, an LLT thin plate, a lithium ion conductive layer, and a lithium metal (negative electrode) was obtained in the same manner as in the examples except that the lithium ion conductive layer was not arranged between the LLT thin plate and the sulfur positive electrode. It was.
Next, the laminate obtained above was placed in a commercially available stainless steel battery cell container, and finally the top lid was closed.
From the above, a battery cell for evaluation was obtained.

<Evaluation of battery characteristics>
The battery cells obtained in Examples and Comparative Examples were subjected to a constant current charge / discharge test under the conditions of a cutoff potential of 1.8 V, a current value of 0.2 mA / cm ² , and a temperature of 120 ° C. The discharge curves (measurement results) obtained at this time are shown in FIGS. 2 and 3. FIG. 2 is a diagram showing a constant current charge / discharge test of the battery cells obtained in the examples. FIG. 3 is a diagram showing a constant current charge / discharge test of the battery cells obtained in the comparative example.
From FIGS. 2 and 3, it was confirmed that the battery cells of this example had good battery characteristics as compared with the battery cells of the comparative example.

<Observation of solid electrolyte>
The solid electrolyte was observed before and after the above-mentioned constant current charge / discharge test. Photographs of the solid electrolyte before and after the constant current charge / discharge test are shown in FIGS. 4 and 5. FIG. 4 is a photograph showing the solid electrolyte before the constant current charge / discharge test. FIG. 5 is a photograph showing the solid electrolyte after the constant current charge / discharge test.
From FIGS. 4 and 5, it was confirmed that the color of the solid electrolyte changed before and after the discharge.
Therefore, when the composition of the solid electrolyte before discharge and the solid electrolyte after discharge was analyzed by an ICP analyzer, the solid electrolyte before discharge was Li _0.35 La _0.55 TiO. _{It was 3} and the solid electrolyte after discharge was found to be Li _1.35 La _0.55 TiO ₃ . That is, it was confirmed that the composition of the solid electrolyte changed between before and after the discharge.

The present invention can be used in the entire field of lithium-sulfur solid-state batteries.

1 ... Lithium-sulfur solid-state battery, 11 ... Sulfur positive electrode, 12 ... Lithium negative electrode, 13 ... Solid electrolyte, 14 ... 1st lithium ion conductive layer, 15 ... 2nd lithium ion conduction layer

Claims (4)

A sulfur positive electrode, a lithium negative electrode, a solid electrolyte containing metal ions reduced by sulfur, and a lithium ion conductive layer are provided.
The solid electrolyte is arranged between the sulfur positive electrode and the lithium negative electrode.
The lithium ion conductive layer includes a first lithium ion conductive layer arranged between the solid electrolyte and the sulfur positive electrode, and a second lithium ion conductive layer arranged between the solid electrolyte and the lithium negative electrode. Including
The first lithium ion conductive layer contains an ionic liquid and conducts lithium ions between the solid electrolyte and the sulfur positive electrode.
The second lithium ion conductive layer is a lithium sulfur solid-state battery that contains an ionic liquid and conducts lithium ions between the solid electrolyte and the lithium negative electrode. The lithium-sulfur solid-state battery according to claim 1, wherein the first lithium ion conductive layer contains polyimide or glass as a constituent material thereof. The lithium-sulfur solid-state battery according to claim 1 or 2, wherein the ionic liquid is a solvated ionic liquid composed of a glyme-lithium salt complex. The lithium-sulfur solid-state battery according to any one of claims 1 to 3, wherein the constituent material of the solid electrolyte is an oxide-based material.